For example, in an air-conditioning apparatus using a refrigeration cycle (heat pump cycle), a heat source side unit (heat source unit, outdoor unit) including a compressor and a heat source unit-side heat exchanger and a load-side unit (indoor unit) including a flow rate control device (such as an expansion valve) and an indoor unit-side heat exchanger are connected to each other by refrigerant pipes to construct a refrigerant circuit for circulating refrigerant. Then, a phenomenon that the refrigerant is evaporated or condensed in the indoor unit-side heat exchanger by receiving or transferring heat from or to air in an air-conditioned space, which is a heat exchange target, is used to condition the air while a pressure, a temperature, and the like of the refrigerant in the refrigerant circuit are changed. In this case, for example, there is known an air-conditioning apparatus capable of performing a simultaneous cooling and heating operation (cooling and heating mixed operation) in which a plurality of indoor units can each automatically determine whether cooling or heating is suitable in accordance with a temperature set by a remote controller (not shown) provided to the indoor unit and an air temperature around the indoor unit, thereby being capable of performing cooling and heating by each indoor unit.
In addition, the following air-conditioning apparatus to be installed in cold districts or the like is known. In order to enhance a heating capacity (the amount of heat (per time) to be supplied to the indoor unit side through a refrigerant cycle by a compressor in heating; the capacities including a cooling capacity are hereinafter referred to as “capacity”) when the outdoor air (hereinafter referred to as “outside air”) is low, the air-conditioning apparatus is added with a circuit for causing refrigerant to flow (for injecting refrigerant) into an intermediate portion of a compression stroke of the compressor provided in the heat source unit through an injection pipe (see, for example, Patent Literature 1).
In the air-conditioning apparatus disclosed in Patent Literature 1, the injection is performed to increase the density of the refrigerant to be discharged from the compressor, to thereby enhance the capacity. Further, at the same time, in the case where the ratio of the number of indoor units that perform heating (hereinafter referred to as “heating indoor units”) among all the indoor units in the cooling and heating mixed operation is high (heating main operation), an evaporating pressure in an indoor unit that performs cooling (hereinafter referred to as “cooling indoor unit”) is controlled by a heat source unit-side flow rate control device.
In this kind of air-conditioning apparatus that is capable of performing the cooling and heating mixed operation and that performs the injection, if the heating capacity is enhanced so as to suit the heating indoor unit, the pressure of the refrigerant on the refrigerant outlet side of the indoor side heat exchanger serving as an evaporator is increased in the cooling indoor unit as well to reduce the pressure difference, with the result that the cooling capacity supplied to the cooling indoor unit is reduced. Thus, the control of the evaporating pressure in the cooling indoor unit by the heat source unit-side flow rate control device in the heating main operation as disclosed in Patent Literature 1 can avoid the problem of the reduction in cooling capacity, thereby securing (maintaining) the cooling capacity.